Effects of Fiber and Ratio of Starch to Sugar on Performance of Ruminating Calves

2~ 5 X 2 factorial experiment determined the effects of five levels of fiber (5 to 60% straw; equal parts of barley, rye, and wheat) and two ratios of starch to sugar (1:1 and 3:1) on the performance of young ruminating calves. Forty male Holstein calves were assigned to ten rations at eight weeks of age and continued on the respective ration for 12 weeks. Feeding was ad libitum. Ratio of starch to sugar had no effect on animal performance. Live weight gains were satisfactory for calves eight to 20 weeks of age on rations containing up to at least 23% aciddetergent fiber. Fill (contents of retieulorumen, onmsum, and abomasum) increased linearly with the dietary fiber level, resulting in a smaller proportion of live weight gain being attributable to true tissue gain on higher fiber rations. Feed intake was maxinmm for the 23% acid-detergent fiber ration and dry matter digestibility was 70% for this ration. Dry matter and crude protein digestibility decreased linearly with fiber content. Fiber digestibility increased with dietary fiber and was maximum for a ration containing 29% aciddetergent fiber. Efficiency of conversion of digestible dry nmtter to body weight gain corrected for fill was similar for all fiber levels.